Here is quite detailed explanation - Flint and Steel Notes – Some Clarifications
by Rob Bicevskis

Originally Posted By: scafool

The magnesium is added as an oxide and is just there to make the rod more brittle so it is easier to scrape sparks off of.


Regarding Aurora firestarter that I mentioned above this is not the case. A big amount of magnesium is integrated directly into the rod so when you strike you throw chunks of burning magnesium. The magnesium is there to make it more powerful.